1. Technical Field
The present invention relates to wireless communications and, more particularly, to detecting and accessing radio networks.
2. Description of Related Art
More people than ever are using mobile stations, such as cell phones and personal digital assistants (PDAs), to connect to wireless wide area networks (WWANs), which are also referred to as cellular wireless communication systems, cellular wireless networks, and by other names. WWANs typically provide both voice and packet-data communication using a wireless communication format such as Code Division Multiple Access (CDMA), or another format.
Mobile stations (such as cell phones) typically store a “preferred roaming list” (PRL), which includes a prioritized listing of communication systems (such as WWANs) that the mobile station may access. In a CDMA system, for instance, a PRL typically includes (i) an acquisition table that instructs the mobile station which radio frequency (RF) channels to search and (ii) a system table that specifies, for each allowed system, a respective system identification code (SID) and network identification code (NID). Each CDMA base station broadcasts its SID and NID in system overhead messages. Thus, when a mobile station detects an allowed SID-and-NID combination, the mobile station may connect to the identified system.
In practice, an initial or default PRL is typically loaded into a mobile station before a wireless carrier distributes the mobile station to a subscriber. The carrier may thereafter load a new PRL into the mobile station at a customer service center or over the air, using over-the-air service provisioning (OTASP), as defined by industry standard EIA/TIA IS-683-C, “Over-the-Air Service Provisioning of Mobile Stations in Spread Spectrum Systems,” published Mar. 20, 2003, which is incorporated herein by reference. In operation, then, mobile stations connect with various WWANs listed on their PRLs according to the listed priorities, and perhaps according to other decision logic and arbitration logic stored in the mobile station.
In addition to WWANs, wireless local area networks (WLANs) are becoming increasingly popular. WLANs typically cover an area that is geographically smaller than that covered by a typical WWAN, and often provide a signal in that area that is superior to that provided by the WWAN. For example, a WLAN may cover a single residence (such as an apartment), a single building, or a proximally-located group of buildings, perhaps on a corporate or academic campus. WLANs typically provide one or more “access points,” which provide a wireless coverage area and access to a packet-data network. A common use of a WLAN is packet-data communication by a wireless-communication-capable laptop computer, or perhaps by another device such as a digital video recorder (DVR) or another appliance or computer. A commonly-used protocol for wireless communication between and among these access points and devices is IEEE (Institute of Electrical and Electronics Engineers) 802.11x
Recently, the telecommunications industry has witnessed widespread growth in the area of voice-over-IP (VoIP) technology; that growth, combined with the ever-increasing prevalence of mobile stations engaging in packet-data communication generally, has caused the industry to begin to introduce mobile stations (“multi-mode devices”) that are equipped to engage in both (i) voice and packet communications via WWANs (using, e.g., CDMA) and (ii) packet-data communications (including VoIP communications) via WLANs (using, e.g., IEEE 802.11x).
In one arrangement, for instance, a cellular wireless carrier may operate a gateway that provides connectivity between a packet-switched network and the wireless carrier's transport and signaling networks. The carrier may then distribute to its subscribers multi-mode devices, which may be capable of communicating in a WWAN mode with one or more types of WWANs and of communicating in a WLAN mode with one or more types of WLANs.
When a multi-mode device is within the coverage area of the carrier's WWAN infrastructure, the device may operate conventionally as a standard cellular telephone, with signaling passing through the carrier's signaling network and bearer data passing through the carrier's transport network. When the multi-mode device moves into the coverage area of a WLAN access point, on the other hand, the device may engage in IP-based signaling and IP-based bearer communication with the carrier's gateway, which may then interface the signaling and bearer communications with the carrier's signaling and transport networks.
PRLs can be extended to the context of multi-mode devices. In particular, a PRL stored by a multi-mode device may list (in the acquisition table) one or more WLAN frequencies and (in the system table) one or more WLAN service set identifiers (SSIDs) (each, in effect, an identifier of a WLAN system) that the multi-mode device may access. More particularly, for each WLAN access point that the multi-mode device is allowed to access, the PRL may list an SSID and MAC (Media Access Control) address of the access point. Thus, when the multi-mode device enters the coverage area of such a WLAN, the device may detect an SSID authorized by its PRL, and may responsively work to associate with the access point.
In general, a multi-mode device may enter the coverage area of a particular WLAN access point that may or may not be listed on the device's PRL. Independent of whether the device's PRL authorizes the device to use this particular WLAN, the multi-mode device may be capable of such access, perhaps for free (such as at a friend's apartment), or perhaps for a fee (such as in an airport or coffee shop). And, this particular WLAN access point may, at that location, provide a stronger signal, less expensive communication, or some other advantage over the WWANs and perhaps one or more WLANs found on the device's PRL. It may, therefore, be advantageous for the multi-mode device to be able to communicate via the particular WLAN—and not via a WWAN or another WLAN listed on the device's PRL—for some amount of time.